The present invention relates to a process for recovering polymetal compounds discharged from a submarine hydrothermal source and to devices for carrying out this process.
From 1977 to 1979, hot sources and accumulations of the above-mentioned substances around these sources have been observed in several occurrences during surveys from submersibles at various points of the Pacific ridge and by floors of about 2800 meters.
The temperature of the water issued from these sources varies between 10.degree. and 350.degree. C. and the deposited products comprise, depending on the temperature, iron or manganese oxides, calcium and barium sulfates, silica and sulfides of such metals as Fe, Zn, Cu, Pb, Ag.
According to the geophysicists, these sources correspond to a circulation of the sea water through the network of fractures of the oceanic ridges. Sea water, when penetrating into rock masses would warm up and dissolve a certain number of elements which have been more or less well integrated during the cooling down of the basaltic magma.
By convection the hot waters would rise up to the surface at speeds varying in accordance with the fracturation state.
At emergence, the more or less abrupt temperature decrease, resulting from the contact with the sea water, would induce a fractionated precipitation of the dissolved substances. Thus, sources at 300.degree.-350.degree. C. would be capable of raising up sulfides, whereas at about 200.degree. C., the latter would have been probably deposited within the rock and only sulfates would be observed. Waters at 20.degree. C. would carry therewith only infinitesimal amounts of the most soluble materials.
Consequently, only sources at high temperature, of present or of fossil origins, may be of economic interest over a long period and may constitute a non-negligible source of raw materials in spite of their sporadic distribution and of their episodic operation. The latter moreover, would be of about ten years, thus substantially the same as the exploitation period of a metal mine.